Space-based solar power (SBSP) describes the collection of solar power in space by a solar-power satellite or a satellite power system (SPS) and then the conversion and transmission of the power to a remote receiver for conversion back to electrical power. In an SBSP system, solar energy is collected as electrical energy on board, powering some manner of wireless power transmission to a receiver located remotely from the SBSP. The wireless power transmission application might include a microwave transmitter or laser emitter, which would direct its beam toward a collector, such as a power receiving rectenna at the remote location, such as, on the Earth's surface.
SBSP differs from ground-based solar collection methods in that the means used to collect energy resides on an orbiting satellite instead of on the Earth's surface. Basing such a system in space results in a higher collection rate for the solar energy due to the lack of a diffusing atmosphere. In a conventional ground-based system a large percentage (55-60%) of the solar energy is lost on its way through the atmosphere by the effects of reflection and absorption. Space-based solar power systems convert solar energy to a far-field emission such as microwaves outside the atmosphere, avoiding these losses. In addition, SBSP systems have a longer collection period and the ability to collect solar energy continuously without the downtime (and cosine losses, for fixed flat-plate collectors) that result from the Earth's rotation away from the sun.
A general limitation for conventional SBSP systems is the size of SPS required to generate sufficient electrical power from solar energy. For example, for a 500 MW system a 5 km2 platform may be required. Such a platform would be formed of large satellites on the order to tens to hundreds of tonnes/satellite. The launch costs associated with placing such large structures into orbit reduces the economic viability of such SBSP systems.